Superoxide dismutase gene expression in skeletal muscle: fiber-specific adaptation to endurance training

The effects of endurance training on the enzyme activity, protein content, and mRNA abundance of Mn and CuZn superoxide dismutase (SOD) were studied i n various phenotypes of rat skeletal muscle. Female Sprague-Dawley rats wer e randomly divided into trained (T, n = 8) and untrained (U, n = 8) groups. Training, consisting of treadmill running at 27 m/min and 12% grade for 2 h/day, 5 days/wk for 10 wk, significantly increased citrate synthase activi ty (P < 0.01) in the type I (soleus), type IIa (deep vastus lateralis, DVL) , and mixed type II (plantaris) muscles but not in type IIb (superficial va stus lateralis, SVL) muscle. Mitochondrial (Mn) SOD activity was elevated b y 80% (P < 0.05) with training in DVL. SVL and plantaris muscle in T rats s howed 54 and 42% higher pooled immunoreactive Mn SOD protein content, respe ctively, than those in U rats. However, no change in Mn SOD mRNA level was found in any of the muscles. CuZn SOD activity, protein content, and mRNA l evel in general were not affected by training, except for a 160% increase i n pooled CuZn SOD protein in SVL. Training also significantly increased glu tathione peroxidase and catalase activities (P < 0.05), but only in DVL mus cle. These data indicate that training adaptations of Mn SOD and other anti oxidant enzymes occur primarily in type IIa fibers, probably as a result of enhanced free radical generation and modest antioxidant capacity. Differen tial training responses of mRNA, enzyme protein, and activity suggest that separate cellular signals may control pre- and posttranslational regulation of SOD.